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🌿 Lichen Symbiosis Growth

A composite organism grows as fungal hyphae branch outward while embedded algal cells convert light into photosynthate that fuels further hyphal extension — mutualism made visible.

Biology & Life2DEasy60 FPS

How it Works

Growth starts from a single central thallus point. Each active hyphal tip extends forward a short step every few frames, and on each step it may also branch into two new tips or stop extending, with branch/stop probabilities shaped by a branching-angle slider. Crucially, the probability and speed of extension are not constant — they are scaled by the locally available "photosynthate" concentration, a resource pool that only algal cells produce. Algal cells are scattered through and around the growing mesh at a density you control; each one generates photosynthate at a rate proportional to the global light level, then diffuses a fraction of it to hyphal tips within a short radius, giving those tips a growth boost.

Algal cells that end up buried deep inside a dense tangle of hyphae are self-shaded: the more hyphal segments crowd within a small radius of a given algal cell, the less usable light reaches it, so its photosynthate output is reduced. A moisture slider scales the overall growth rate multiplicatively, reflecting how lichens are poikilohydric — they have no roots and can only grow while their tissue is hydrated, going dormant when dry. The net effect is a thallus that visibly bulges outward faster wherever more, better-lit algal cells happen to be embedded, and stalls in algae-poor or self-shaded regions.

photosynthate(cell) = lightLevel · (1 − shadeFactor(cell)), shadeFactor ∝ nearby hyphal segment count
tipExtendProb = baseProb · moisture · (1 + Σ nearby photosynthate / normFactor)
On extension: branch into 2 tips with prob pBranch(branchAngle), else continue straight, else stop
new tip angle = parentAngle ± U(0, branchAngle)

Frequently Asked Questions

What is a lichen?

A lichen is a composite organism formed by a symbiotic partnership between a fungus (the mycobiont, providing structure and mineral uptake) and a photosynthetic partner, usually green algae or cyanobacteria (the photobiont, providing sugars from photosynthesis).

What is the mycobiont and photobiont relationship?

The mycobiont (fungal partner) forms the bulk of the lichen's structure and protects and anchors the photobiont, while the photobiont (algal or cyanobacterial partner) supplies sugars produced through photosynthesis that fuel the fungus's growth. Both partners benefit, making this a classic mutualism.

Why does the hyphal network grow unevenly?

Hyphal tips extend faster where locally available photosynthate is higher, which is wherever more or better-lit algal cells are nearby. Areas with sparse or shaded algae starve the fungal tips of sugar, so growth naturally concentrates toward light-rich, algae-dense regions.

Why does moisture matter so much to lichen growth?

Lichens have no roots or vascular tissue and absorb water directly from their surroundings (poikilohydry). Photosynthesis and hyphal extension both require hydrated tissue, so growth essentially pauses during dry periods and resumes when moisture returns.

What is self-shading in this simulation?

Self-shading models how algal cells buried deep inside a dense thallus receive less usable light than those near the growing edge, because surrounding hyphae and overlapping algal cells intercept light before it reaches them, reducing their photosynthate output.

About this simulation

Every grey thread pushing outward from the center is a fungal hypha bidding for space, but none of it moves without sugar from a green algal cell nearby — starve the mesh of light or moisture and growth visibly stalls, feed it and the thallus balloons unevenly toward wherever its photosynthetic partner is thriving, exactly the push-and-pull that keeps a real lichen alive on bare rock for centuries.

🔬 What it shows

A branching-random-walk fungal network whose tip-extension probability is fed by diffusing photosynthate produced by nearby algal cells, with self-shading reducing output for buried algae.

🎮 How to use

Tune Light Level, Moisture, Algal Cell Density and Branching Angle, then watch the thallus grow; press Reset/Reseed or R for a fresh random layout, P to pause.

💡 Did you know?

Lichens are so moisture- and pollution-sensitive that scientists use them as bioindicators, and some Arctic lichen thalli are estimated to be thousands of years old, growing only a few millimeters per century.

Frequently asked questions

What is a lichen?

What is the mycobiont and photobiont relationship?

Why does the hyphal network grow unevenly?

Why does moisture matter so much to lichen growth?

What is self-shading in this simulation?

⚙ Under the hood

A composite organism grows as fungal hyphae branch outward while embedded algal cells convert light into photosynthate that fuels further hyphal extension — mutualism made visible.

Canvas 2DLichenSymbiosisMycobiontPhotobiont

2D · HTML5 Canvas 2D · 60 FPS target · runs fully client-side, no install